Two tools in one. The historical mode answers the question people actually type, what is $100 from 1990 worth today, using the actual annual CPI-U record back to 1913. The projection modes answer the planning question, what will my money buy in twenty years, at whatever rate you assume, because nobody knows future inflation and a calculator that pretends to is lying. The page is clear at every step about which kind of answer you are getting.
Two kinds of question, kept honestly apart
The historical mode is a real CPI lookup: it carries the Bureau of Labor
Statistics' annual-average CPI-U for every year from 1913 through 2025, so "what is
a 1980 dollar worth today" gets answered from what prices actually did, not from an assumption. The
two projection modes are the opposite kind of tool on purpose: a fixed-rate
projection for planning, where you pick the rate (the long-run US average works out to
about 3.2% a year) because nobody knows future inflation and honest planning means choosing
assumptions in the open. Every result says which kind of answer it is.
The formulas
Between two years = Amount × CPI(to year) ÷ CPI(from year)
Future buying power = Amount ÷ (1 + r)t Future cost = Amount × (1 + r)t
The historical formula is a ratio of price levels: the CPI-U averaged 130.7 in 1990 and 321.9 in
2025, so 1990 money multiplies by 321.9 ÷ 130.7 = 2.46 to land in today's terms. The
projection formulas compound your assumed rate r for t years, the same exponential curve as
interest, working against you instead of for you.
How to calculate the inflation rate from the CPI
Inflation rate = (CPI this year - CPI last year) ÷ CPI last year × 100
The published inflation rate is nothing more mysterious than the percent change in the Consumer
Price Index. The CPI-U averaged 313.7 in 2024 and 321.9 in 2025, so the 2025 rate is
(321.9 - 313.7) ÷ 313.7 × 100, which is about 2.6%. Every yearly rate in this
calculator's table is that same subtraction and division, run on the BLS annual averages.
Worked examples, one of each kind
History: $100 from 1990 is worth $246.29 in
2025, prices having multiplied 2.46x across 35 years, an average of 2.61% a year.
Stretch to the table's far end and $100 from 1913 becomes about $3,252.
Projection: $100 at an assumed 3% for 20 years:
buying power shrinks to $55.37, while today's $100 price tag grows to
$180.61. Same curve, read in opposite directions.
What the table remembers that folklore forgets
Deflation happened, and the historical mode reports it faithfully: prices fell from 1920 to 1933
with only brief pauses, so $100 of 1920 goods cost about $64.50 by 1933, and the
annual index slipped again in 2009. The 1970s remain the cautionary decade, prices more than
doubling from 1970 to 1980. And the index carries one modern oddity: the October 2025 CPI
was never published, the first gap in the modern record, because that month's government
shutdown halted collection; annual averages, which this page uses, absorb it gracefully.
Where the numbers come from, and how we check them
The table is the BLS CPI-U, all items, annual averages, on the 1982-84 = 100
base, the same series behind the Federal Reserve's own inflation calculators. The base period is
also our built-in audit: the 1982, 1983 and 1984 entries average to exactly 100.0,
which is what that base definition promises, and our test suite refuses to ship the page unless
they still do. The record's final year advances each January when BLS closes out the annual
average.
Two questions, one curve
The projection modes are the same math read in opposite directions, and people constantly mix
them up. Buying power holds the dollars fixed and shrinks what they buy; use it to judge
cash sitting in a low-interest account. Future cost holds the goods fixed and inflates the
price tag; use it to set savings targets. The rule of 72 is the useful shortcut: at 3%, prices
double and idle cash halves roughly every 24 years. The historical mode is the proof this is not
theoretical: a 1990 mattress dollar buys about 41 cents of 1990's goods today, which is the whole
argument for the compound interest calculator and the
S&P 500 calculator in a single number.
Frequently asked questions
What is $100 in 1990 worth today?
About $246 in 2025 dollars. The CPI-U averaged 130.7 in 1990 and 321.9 in 2025, so prices multiplied by about 2.46 over those 35 years, an average of 2.61 percent a year. The between-two-years mode runs this for any pair of years back to 1913, where the answer becomes about $3,252 for the same hundred dollars.
Does this calculator use real historical inflation data?
The between-two-years mode does: the actual annual-average CPI-U for every year from 1913 through 2025, the Bureau of Labor Statistics' urban consumer index that official inflation figures come from. The two projection modes deliberately do not; they compound a rate you choose, because future inflation is unknown and honest planning means picking assumptions in the open. The page always says which mode you are in.
Where does the CPI data come from?
The BLS Consumer Price Index for All Urban Consumers (CPI-U), all items, as annual averages on the 1982-84 = 100 base, the same table the Federal Reserve's own inflation calculators use. Our copy is checked against the index's own definition: the 1982, 1983 and 1984 values in the table average to exactly 100.0, which is what that base period means.
Why annual averages instead of a specific month?
Because when someone asks what 1975 money is worth, they mean the year, not one Tuesday of it. Annual averages smooth the seasonal wiggle and match how the question is asked. It also sidesteps a genuine oddity: the October 2025 CPI was never published, the first gap in the modern record, because the government shutdown that month stopped the data collection. Yearly figures shrug that off.
Has the US ever had deflation?
Yes, and the table remembers it. Prices fell from 1920 through 1933 with only brief pauses, so $100 of 1920 goods cost about $64.50 by 1933, the only long deflation in the record. It happened again briefly in 2009, when the annual index slipped from 215.3 to 214.5. Run those year pairs and the calculator reports prices falling, because that is what happened.
What inflation rate should I use for planning?
The long-run US average since 1913 works out to about 3.2 percent a year, which is why 3 percent is the common planning default. Recent decades ran closer to 2 to 2.5 percent with a sharp spike in 2021 and 2022. Running the projection at 2, 3 and 4 percent gives a realistic range rather than one falsely precise answer.
What's the difference between the two projection modes?
Future buying power answers 'what will my $1,000 really be worth?' It divides by (1+r)^t, so the number shrinks. Future cost answers 'what will something costing $1,000 today cost later?' It multiplies by (1+r)^t, so the number grows. Same math, opposite directions.
Why does inflation matter for my savings?
Cash that earns less than inflation is quietly losing value every year. At 3 percent, idle money loses roughly half its buying power in about 24 years (the rule of 72). The historical mode makes this concrete: a dollar put under a mattress in 1990 buys about 41 cents of 1990's goods today, which is the argument for our compound interest and S&P 500 pages in one number.